As sea levels rise, coastal wetlands around the world are expected to shrink – and researchers at the University of British Columbia have found this could put the world's shorebirds and their critical habitat at risk.
The first global systematic review of its kind, published in Biodiversity and Conservation , examined the impacts of rising sea levels on 29 species of shorebirds, including plovers, sandpipers and oystercatchers. The review found rising seas are expected to have predominantly negative impacts on shorebird habitat and populations, while human infrastructure could make the problem worse by preventing coastal wetlands from moving inland.
"As sea levels rise, coastal wetlands need space to retreat, but many of the places where shorebirds depend on these habitats are already constrained by dykes, roads and other development," said lead author Jennifer Magel, a PhD student at the Faculty of Forestry & Environmental Stewardship at UBC. "If we continue to develop our coastlines without considering where these wetlands can go, we risk losing important shorebird habitat."
The researchers reviewed 37 studies that included data on the effects of sea level rise on shorebirds: 78 per cent found negative impacts on habitat, while 89 per cent found negative impacts on shorebird populations or individual birds.
Giving wetlands room to move
The review highlights a conservation challenge known as coastal squeeze: as seas rise, wetlands need to move inland, but dykes, roads, buildings and other infrastructure block that retreat. In areas without human barriers, wetlands can migrate inland. But where coastal development or shoreline armouring blocks that movement, habitat can become trapped against a fixed shoreline.
"This is the crux of the issue," said co-author Dr. Tara Martin, a professor in the Faculty of Forestry & Environmental Stewardship at UBC. "As we shore up our shorelines to protect human infrastructure, we're decreasing the available habitat for all the animals that use this intertidal zone."
More than just habitat loss
The review suggests the consequences for shorebirds may extend beyond simply losing habitat. In eight of nine studies that examined both habitat and population impacts, projected population impacts were more severe than would be expected from habitat loss alone.
Shorebirds may travel anywhere from hundreds to tens of thousands of kilometres during migration, stopping at tidal flats and other coastal habitats to rest and feed before continuing their journeys. In B.C., the Fraser River Estuary acts as a critical bottleneck where large numbers of birds converge in a relatively small area to replenish the energy they need to migrate along the Pacific Flyway.
Rising seas can reduce the amount of time tidal flats are exposed for feeding, while changes in sediment, salinity and water depth can alter prey availability. For nesting birds, higher water levels can also increase the risk of nest flooding.
"Shorebirds rely on these coastal habitats as places to rest and refuel during their migrations," said Magel. "If one of these important stopover sites is affected, it can have consequences for an entire population of birds because so many of them rely on these bottleneck sites."
Planning for rising seas
Although many studies examined impacts projected toward the end of the century, the researchers emphasize that coastal adaptation decisions need to be made now.
They urge planners to protect space inland of existing wetlands, remove or alter artificial barriers, enhance sediment supplies and, where appropriate, consider managed coastal retreat. The researchers point to the Sturgeon Bank Sediment Enhancement Pilot Project in the Fraser River Estuary as an example of testing how sediment can build wetland elevation to support coastal habitat.
"The earlier we act and take these nature-based coastal adaptation approaches, the more space we will have for these wetlands to move and the more habitat we'll save for the future," said Dr. Martin.
Interview languages: English (Magel, Martin)
